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The high pressure die casting process is extensively used to manufacture light metal parts with high productivity. A major drawback of the process is the relatively high variability in mechanical properties and poor repeatability between casting cycles, limiting the achievement of weight reduction through lighter design. Although it has been establ...
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... the solid crystals were not directly modelled in this approach, solid formation in the sleeve could be predicted. Figure 3 shows the evolution of the solid fraction prior to melt injection. It could be seen that solid forms near the piston and at the bottom of the sleeve due to rapid cooling. ...
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... Most of the gases are pushed from the filling chamber in front of the melt flow face out of the filling chamber and subsequently out of the mold through the venting system. Part of the gases in the filling chamber can be trapped in the melt volume, while the gas entrapment volume is largely determined by the shape of the generated wave [9]. The reduced velocity in the first phase of the piston movement is beneficial for the continuous expulsion of gases from the filling chamber of the machine. ...
... A certain amount of gases are trapped in the cast as a result of the filling mode of mold cavity. In real conditions, the filling mode of the mold cavity achieved is showing turbulent flows with dispersive character [9][12] [13]. ...
... The process was repeated in the ProCAST® software with the efficiency having been proven by obtaining a casting no defects. Dou et al. [15] developed a numerical simulation approach also based on the ProCAST® finite element casting software, having carried out a study of fluid flow, solidification and defect formation during each stage of the high-pressure casting process: casting, injection and cooling. Air trapping and porosity distribution in the casting were foreseen. ...
Comparisons between virtual prototyping and experimental results are notably beneficial for the development of investment casting processes. In this research, such a comparison aimed to study the castability of a Cu-Al-Mn shape memory alloy (SMA) in a modified centrifugal investment casting process that uses centrifugal force to inject the molten metal into the mold. Virtual prototyping was numerically simulated using the ProCAST software applying a rectangular mesh part design. The real and virtual parts were examined for mold filling (castability), pore formation, and solidification time. Using Whitlook’s methodology, it was possible to validate the model created in the ProCAST software to simulate the modified investment casting process, detecting results regarding filling, solidification, and porosity with a high degree of accuracy and reliability. In addition to the validation of the developed model, this work also presents estimated values for interface heat transfer coefficient (IHTC) of the metal/mold of aluminum bronze (Cu-Al and Cu-Al-Mn) alloys poured by gravity and centrifugation into plaster molds. Among the obtained values, the IHTC for the 86.7Cu-7.9Al-5.4Mn SMA were estimated at 535 W/m² K when poured by centrifugal force and 75 W/m² K by gravity. Ultimately, it was possible to verify that Cu-Al-based shape memory alloy presents a high castability and a low cooling rate.
... Previous investigations into the variable properties of die castings can be broadly divided into three categories: (i) those that relate the variability in tensile ductility to statistical variations in melt quality [8][9][10]12]; (ii) those that derive empirical correlations between the tensile ductility and various measures of microstructural heterogeneity [5][6][7][13][14][15]; and (iii) those that consider the stochastic nature of fluid flow and the subsequent encapsulation of air and oxides [16][17][18][19]. While porosity is a recurrent theme in these studies, its formation mechanism is widely disputed. ...
... With advanced parallel computing techniques, and a variety of mathematical models, physical phenomena including fluid flow, heat transfer, solidification, and defect formation can be modelled in a timely and detailed manner. Dou et al. [19,21,22] modelled the HPDC process using the finite element method (FEM) under the ProCAST (ESI Group) software platform. An overview of the modelling procedure is presented in the following paragraphs, with detailed accounts provided in references [19,21,22]. ...
... Dou et al. [19,21,22] modelled the HPDC process using the finite element method (FEM) under the ProCAST (ESI Group) software platform. An overview of the modelling procedure is presented in the following paragraphs, with detailed accounts provided in references [19,21,22]. ...
This article provides an overview of high-pressure die casting (HPDC)-related research undertaken at the EPSRC Future LiME Hub between 2015–2022. The project aimed to identify the cause of variability in the tensile ductility of die-cast structures, and to develop novel processing techniques to address this issue. Variability in tensile ductility was related to the size of large pores and non-metallic inclusions. It was proposed that these non-metallic inclusions formed during the pyrolysis of commercial plunger lubricants in the shot sleeve, and that these large pores derived from dilatational strains introduced during semi-solid deformation. Processing parameters and die design were found to significantly influence the microstructure of die-cast products, and the subsequent variability in tensile ductility. To close, recent progress on the application of intensive melt shearing to HPDC is reviewed. Intensive melt shearing was found to induce significant grain refinement in both Al and Mg alloys due to the effective dispersion of native oxide particles, and the use of these particles as heterogeneous nucleation substrates. The presence of native oxide particles also enabled the use of novel heat treatment procedures that avoided conventional issues such as surface blistering and geometrical distortion.
... Die-casts are characterized by high geometric accuracy, good mechanical properties and low price. Good mechanical properties of casts are related to their fine-grained structure, caused by subcooling of the melt in contact with the relatively cold wall of the mold cavity [2], but defects of casts related to porosity and the presence of gases in the melt significantly affect the quality of casts [3,4]. ...
One of the most important indicators of casting quality is porosity. The formation of pores is largely conditioned by the presence of hydrogen in the batch and subsequently in the melt. The gasification of the melt is the primary factor increasing the porosity of casts. This paper addresses the issue of reducing the melt gasification by using FDU (Foundry Degassing Unit) unit. The gas content in the melt is evaluated by determining the Dichte Index depending on the geometry and the degree of the FDU unit rotor wear. For experiments performed under the operating conditions, three types of graphite rotors with different geometries are used. The extent of melt gasification and the Dichte Index are monitored during the rotor wear, at a rate of 0%, 25%, 50%, 75% and 100% rotor wear. Secondly, the chemical composition of the melt is monitored depending on the design and wear of the rotor. It is proven that the design and the degree of rotor wear do not have significant effect on the chemical composition of the melt and all evaluated samples fell within the prescribed quality in accordance with EN 1706. With regard to the overall comparison of the geometry and wear of individual rotor types, it has been proven that, in terms of efficiency, the individual rotors are mutually equivalent and meet the requirements for melt degassing throughout the service life.
... The filling and solidification in the shot sleeve of the CC-HPDC machine is modeled using finite element method (FEM) and can be found in the previous works of the authors. [12][13][14] The calculation domain which takes into account the entire HPDC machine is shown in Figure 1. A detailed view of the shot sleeve region is shown in Figure 2. The general FEM mesh size for the entire domain is 1mm, while in the specific thin regions such as in gate and runner, the mesh size of 0.2mm is used. ...
In the cold chamber high-pressure die casting (CC-HPDC) process, alloy solidification in the shot sleeve due to heat loss leads to the formation of externally solidified crystals (ESCs), which have been proven to be closely related to microstructure inhomogeneity and mechanical properties of cast components. In this paper, the solidification behavior of aluminum alloy inside the shot sleeve is studied using a numerical modeling approach. Fluid flow, heat transfer, and solidification of aluminum alloy melt inside the shot sleeve are studied using ProCAST software in three dimensions. A comparison between modeling and experiments shows good correspondence. Moreover, the evolution and distribution of ESCs in the shot sleeve along with their dependence on the piston motion profile are analyzed accordingly. The results show that after the melt impinges the shot sleeve wall, a thin layer of initial solid forms on the wall with a non-uniform distribution along the sleeve in both the longitudinal and radial directions. With piston movement, the initial solid fraction first increases and then decreases to some extent before being injected into the die cavity. The amount of ESCs at the melt free surface are quantitatively analyzed and validated for different piston motion profiles. The results of this work would be useful in further microstructure and mechanical property variability study of high-pressure die casting products.
... Casts produced in the die casting process are characterized by high geometrical precision, good mechanical properties, and low price. Mechanical properties of casts are closely related to formation of fine-grained structure in the case of fast melt cooling with the mould face [2]; however, defects such as porosity, primarily caused by air entrapment by the melt during the filling phase, significantly influence the quality of casts [3]. ...
Quality properties of castings produced in a die casting process correlate with porosity that is conditioned by a number of factors, which range from input melt quality to setup of technological factors of the die casting, and through structural design of the gating system. One of the primary parameters conditioning the inner soundness of the casting is the liquid metal dose per single operation of die casting. This paper examines the issue of metal dose. The experiments are performed with casting a gate system of an electromotor flange. The gating system examined was die cast with a variable volume of metal dose per single operation. The metal dose was adjusted to reach the height of a biscuit of 10, 20, and 30 mm. The examination of the inner homogeneity of the castings of the individual variants of gating systems with variable height of the biscuit proved that decreasing biscuit height results in an increase of porosity share in the casting volume. The programme MagmaSoft 5.4 revealed the main causes of changes in porosity share. The simulations detected that the change in biscuit height and volume of liquid metal directly influence thermal conditions of the melt in the filling chamber, and in the mould by means of the period in which the holding pressure action is influenced. Simultaneously, the melt flow mode in the sprues and gas entrapment in the melt volume are affected as well. Correlation of the factors consequently influences the final porosity of castings.
... The HPDC process was simulated using a finite element model developed under the ProCAST (ESI Group) software platform. Details of the modelling procedure are outlined in our previous paper [25] . In short, governing equations for mass, momentum, and heat (based on the enthalpy method) are solved in ProCAST [25] . ...
... Details of the modelling procedure are outlined in our previous paper [25] . In short, governing equations for mass, momentum, and heat (based on the enthalpy method) are solved in ProCAST [25] . The volume of fluid (VOF) method is used to monitor the evolution of the melt free surface [25] . ...
... In short, governing equations for mass, momentum, and heat (based on the enthalpy method) are solved in ProCAST [25] . The volume of fluid (VOF) method is used to monitor the evolution of the melt free surface [25] . Fluid turbulence is described using a standard k -turbulence model described in references [ 26 -28 ]. ...
The breakup of agglomerates and bodies suspended in turbulent flows are important phenomena that influence many aspects of modern solidification processing. It is often assumed that breakup operates in high-pressure die casting, wherein molten metal is transported at high speed through a narrow orifice system. To test this assumption, X-ray tomography and electron backscatter diffraction mapping are used to characterise pores, inclusions, and primary α-Al grains in die-cast samples produced with different flow field intensities. Numerical simulations are performed in ProCAST (ESI Group) to quantify the three-dimensional flow fields and to relate the derived quantities to breakage. Increasing the dissipation rate of turbulent kinetic energy is shown to induce a refinement of both non-metallic inclusions and primary α-Al1 grains nucleated in the shot chamber, a phenomenon which is ascribed to breakage. Several breakup mechanisms are discussed, with emphasis on the role of fluid turbulence.
... The second relates the scatter in tensile ductility to statistical variations in melt quality (e.g. chemical composition [11,16], gas content [8], number of inclusions in the melt [9]). The third considers the stochastic nature of fluid flow, and the subsequent encapsulation of air and oxides [17][18][19][20]. Although porosity is a recurrent theme in these studies, its formation mechanism is widely disputed [4,9,13]. ...
This article unmasks the probabilistic nature of high-pressure die casting; specifically, the cause of scatter in the tensile ductility of die-cast Al8Si0.4Mn0.3Mg (wt.%) alloy. Scatter in tensile ductility is related to the size of large pores and non-metallic inclusions. We propose that these non-metallic inclusions form during the pyrolysis of commercial plunger lubricants, and that these large pores derive from dilatational strains introduced during semi-solid deformation. The apparent randomness of pore formation is thus ascribed to the heterogeneous nature of the semi-solid network. Reducing heat loss in the shot chamber is shown to promote a more homogeneous grain structure, leading to a decrease in the maximum pore size from 1.32 mm to 0.37 mm, and an increase in the minimum tensile ductility from 6.8 % to 9.4 %.
... A value of 0.99 corresponds to more slip along the wall, whereas a value of 0.8 will act as if the mold surface is rougher (more friction). In this work, a time-dependent WALLF value is defined based on previous work of the authors (Dou et al., 2019). And it is shown in Fig. 4. ...
Aimed at the mechanical property improvement in the high pressure die casting (HPDC) process for the aluminium alloy, two sets of shot curves (the baseline and the optimized condition) are designed to study their influence on the distributions of the ultimate tensile strength (UTS) and the elongation (El) for the as-cast ASTM tensile samples. Difference in the as-cast microstructures and defects are characterized and compared accordingly. Following the experiments, a mathematical model for the entire HPDC process is established to study the characteristics of the melt flow, heat transfer, solidification and defects formation (entrapped gas, oxides, porosities) during the HPDC process with the two above-mentioned piston shot curves are analyzed. The results have shown that the UTS and the El are improved obviously with the optimized shot profile. And the mechanism for these changes are explained in detail. This work provides a novel approach for designing and optimization of metal casting process without conducting excessive experiments and it could be transferred and applied to various alloys systems and different casting processes.
... Time-dependent iHTCs are then introduced and used in subsequent CAE simulation. Details about previous work can be found in this reference [12]. The evolution of iHTCs is revealed as in Fig. 5. ...
The application of computer aided engineering (CAE) has become a trend in manufacture industry due to its great efficiency and reliability. In casting industries, numerical modelling of the casting process based on CAE has replaced traditional trial-and-error R&D procedures in many aspects. With advanced parallel computing techniques and numerous calculation models, the fluid flow, heat transfer, solidification and defect formation behaviours under different casting conditions may be examined in detail. Based on this idea, component design and the optimization of casting parameters may be carried out to produce products for subsequent microstructural and mechanical characterization. In this way, a direct link between process condition, casting quality, and cast mechanical properties may be established in a manner that is practical, economical and energy efficient for such processes as gravity die casting, high pressure die casting (HPDC) and continuous casting. In this work, the entire HPDC process, including die heating, thermal die cycling, shot sleeve pre-filling, slow shot/fast shot injection, die filling/solidification as well as intensification, is simulated for an Al-Si alloy using the casting simulation package ProCAST. The interfacial heat transfer coefficients between melt and die wall/ shot sleeve are adjusted according to thermal couple measurements and infrared imaging of the die surface temperature distribution. Based on this complete numerical model, the HPDC process may be optimized using the following methodology: 1) the optimum thermal die cycle number is determined after which the dynamic steady state of die temperature is obtained to guarantee relatively sound casting quality. 2) The piston shot profile is adjusted to reduce defect formation during injection. In the meantime, tensile bars are cast using the optimized piston shot profile and the mechanical properties (yield strength, ultimate tensile strength and elongation) are tested to assess the effectiveness of the computer simulation. Results show that the mechanical properties are improved with the optimized process parameters, providing further evidence that CAE could help in the optimization of HPDC processes.
